Disclosed herein are a novel photosensitive copolymer, a photoresist incorporating the copolymer, and a method of making a pattern from the photoresist.
EUV (Extreme Ultraviolet) photoresist development continues to be a challenging issue for EUVL (EUV Lithography) technology implementation. Development of materials that are not only high resolution (i.e., resolving features of 22 nm at half pitch) and with a low linewidth roughness (LWR) of less than 1.8 nm, but sensitive enough to afford high wafer through put are required (i.e., 10-15 mJ/cm2).
For EUV photoresist material and polymer design, a very important consideration is EUV absorption. Polymers widely used for EUV platform are ionized by high energy (13.4 nm) light and release high energy electrons. The high energy electron is trapped by the photoacid generator through reductive electron transfer and activates the PAG to generate acid.
EUV sensitivity is also determined by photo speed, which may be increased by varying the concentration and or efficiency of photoacid generators (PAGs) in the resist, optimizing the number of acid-labile protecting groups on a polymer backbone, engineering the polymer protecting groups, or reducing the base quencher amounts. Sasaki et al. (“Development of partially fluorinated EUV-resist polymers for LER and sensitivity improvement,” T. Sasaki, O. Yokokoji, T. Watanabe and H. Kinoshita, Proc. SPIE V. 6923, 692347, (2008)) disclose introducing halogen atoms into polymers enhances acid generation yield and resist sensitivity in EUV systems, due to an increase in the absorption coefficient by the halogens which are high absorbing EUV elements. This additional absorption can make for efficient use of the incident energy in EUV lithography.